Conventionally, a jacket structure that is utilized as an oil drilling structure is known as a representative example of an underwater frame structure that is installed on the sea bed foundation (for example, refer to Patent Documents 1 and 2). This jacket structure is constituted by moving one that consists of steel legs, horizontal braces and diagonal braces preassembled at an on-shore yard to the installation location, and fixing to the sea bed foundation. Thereby, construction work at the construction site is simplified, and the construction period is shortened.
In this kind of jacket structure, the frame that is constituted from legs and braces is generally manufactured with steel as disclosed in Patent Documents 1 and 2. On the other hand, a jacket structure that has legs and horizontal struts made of reinforced concrete (RC structure) has been proposed (for example, refer to Patent Document 3).
As a connection structure with piles in the above jacket structure, a structure has been adopted that inserts one of a leg and pile into the other, and by filling a grout in mutual gaps in this insertion portion, integrates the leg and the pile. Also, a leg and a horizontal strut with an RC structure disclosed in Patent Document 3 are bolt-connected via a steel joint member. A joint structure is adopted that integrates the leg and the horizontal strut by filling grout or a similar material inside this joint member.